1. Field of the Invention
The present invention relates to a cutting drill for making holes in a printed wiring board, and to a method for manufacturing a printed wiring board using the cutting drill.
2. Discussion of the Background
In response to requirements for making highly integrated printed wiring boards, holes to be formed are becoming smaller. To achieve smaller holes, in a cutting drill a rod-shaped drill section with a small diameter of approximately 0.1-3.175 mm, for example, is fixed to a shank section with a relatively large diameter to grip the drill body in a rotation shaft of a machine tool. A hard cemented carbide alloy is usually used for the drill section. A machine tool for drilling printed wiring boards is equipped with a polishing tool for polishing the cutting drill. When the cutting edge of the cutting drill becomes dull, the cutting edge will be reused by repolishing with the polishing tool. Cutting procedures are conducted through repeated repolishing until such reuse is no longer feasible.
Cutting drills for printed wiring boards are roughly divided into two kinds: a straight type described in Japanese Laid-Open Patent Publication 2002-18623; and an undercut type described in Japanese Laid-Open Patent Publication 2002-137110. In a straight type, a rod-shaped drill section is formed to have a constant diameter. In an undercut type, a rod-shaped drill section is formed to have a diameter approximately 0.01-0.03 mm smaller in the area positioned approximately 1-5 mm down from the tip. In an undercut type, only the blade portion positioned between the tip and the area 1-5 mm down from the tip makes contact with the inner-wall surface of a hole being processed, and the portion with a smaller diameter does not make contact with the inner-wall surface. Thus, the contact area on the surface of the hole being processed may be reduced, and the surface accuracy of the inner-wall surface of the hole being processed may be enhanced. The contents of these publications are incorporated herein by reference in their entirety.